metamorphic
Quartzite
Metamorphic Quartzite (primarily SiO2)
Hardness: 7 on the Mohs scale, Color: White, gray, pink, or reddish due to iron impurities, Luster: Vitreous to greasy on fractured surfaces, Crystal Structure: Interlocking quartz crystals, Cleavage: None (fractures conchoidally through the grains), Specific Gravity: 2.65
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Physical properties
Hardness: 7 on the Mohs scale, Color: White, gray, pink, or reddish due to iron impurities, Luster: Vitreous to greasy on fractured surfaces, Crystal Structure: Interlocking quartz crystals, Cleavage: None (fractures conchoidally through the grains), Specific Gravity: 2.65
Formation & geological history
Formed from quartz-rich sandstone or chert through regional or contact metamorphism involving high heat and pressure, which recrystallizes the quartz grains into a dense, interlocking mosaic.
Uses & applications
Used in construction, railroad ballast, crushed stone for road surfaces, manufacturing of silica brick, and occasionally as a decorative stone or in countertops.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering, which is why mountains made of quartzite often form prominent ridges and peaks.
Field identification & locations
Can be identified in the field by its hardness (scratches glass easily), inability to be scratched by a knife, and the way it fractures across the grains rather than around them like sandstone. Found worldwide.
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